Figure 3.

Germline-biased gene expression in transformed ovaries. (a) Heat diagram (yellow > red > blue) of hybridization intensities for all unique array
element sequences (N = 13,267) from individual samples (columns) used in this study. Gonad samples (left)
and somatic samples (right) are indicated with karyotype (XX;AA and X;AA) and abbreviated
genotypes; wt, wild type (see Materials and methods for more details). Replicates
are indicated (brackets). Germline expression is clearly evident in the gene-expression
profiles of transformed ovaries. There are large blocks of elements showing high-
or low-intensity hybridization to gonad probes and the opposite pattern when hybridized
to samples from carcasses or from flies lacking germ cells but having somatic components
of the gonads. (b) Selected genes with known functions in the germline. Array elements representing germline-marker
genes (for example, vasa (vas), pumilio (pum), tudor (tud), piwi and benign gonial cell neoplasia (bgcn) [67,68]) show strong hybridization to labeled gonad mRNA samples and comparatively
weaker hybridization to non-germline samples. Furthermore, at least some of the differences
between the samples also support the proposed germline sex-determination pathway.
For example, as predicted, both ovo and otu are germline-biased and overexpressed in XX;AA Sxl ovaries relative to X;AA hs-tra ovaries [40,69]. All these data validate the use of XX;AA and X;AA transformed germlines
as matched tissues for the careful analysis of X-chromosome dosage compensation in
the germline.